Fibronectin, a high molecular weight cell surface glycoprotein also found in plasma, amniotic fluid, and cerebrospinal fluid is involved in cell to cell and cell to substrate adhesion. It is lost from or no longer bound to malignantly transformed cells. Fibronectin specifically interacts with collagen, glycosaminoglycans, gangliosides, actin, and DNA. Cell surface and soluble forms of fibronectin differ primarily in their degree and nature of glycosylation, and perhaps in their ability to polymerize into high molecular weight complexes. We propose to study the primary structure of fibronectin by a combination of microsequence analysis of tryptic peptides and molecular cloning of the cDNA corresponding to fibronectin mRNA. These studies in combination with isolation of peptide fragments by affinity chromatography should lead to a structure-function understanding of the molecular domains of fibronectin. An analysis of the primary sequence of fibronectin isolated from several sources and DNA sequencing of the 5' and 3' extensions of the cDNA should give an insight into the mechanism of determining which glycosylation pattern a fibronectin will ultimately have.